A thermal trip device is, for example, a device that detects overcurrent in a circuit breaker to trip a main circuit. Trip characteristic when overcurrent flows has its range stipulated by standard such as JIS (Japanese Industrial Standard) and products need to comply with it. In a thermal trip device, however, variation in trip characteristic is inevitable due to manufacturing variation of constitutional components and material variation. Consequently, a structure for adjusting the trip characteristic is usually incorporated to adjust and inspect the characteristic.
In order to adjust and inspect the trip characteristic, its characteristic value needs to be accurately measured. In the thermal trip device, the trip characteristic is often measured by measuring a time (trip time) from energization initiation to trip completion and an amount of displacement of a bimetal by supplying a predetermined current. Meanwhile, curvature factor of a bimetal is known and therefore the amount of displacement of the bimetal can be determined by measuring a bimetal temperature. Therefore, the trip characteristic can be figured out by measuring the bimetal temperature.
When measuring the bimetal temperature, a method of no-contact measurement is preferable in order not to affect on an amount of curvature of the bimetal by measurement. In measurement by a contact thermometer, load is applied to a bimetal from outside via a probe and therefore deflection is generated in the bimetal to cause change in trip characteristic. As for a method of no-contact temperature measurement, an emission thermometer incorporating an infrared absorption element is commonly used.
However, there is a problem in that a usual bimetal surface is a metallic luster surface and therefore accurate temperature measurement is difficult. Furthermore, in an electric leakage circuit breaker incorporating an electric leakage detection circuit and a circuit breaker reduced in size, it is difficult to measure a temperature of the bimetallic surface from outside because of having fewer clearances around the bimetal.
The present invention is implemented to solve such problems, and an object of the present invention is to provide a thermal trip device and a circuit breaker using the same, capable of highly accurately measuring a bimetal temperature using a no-contact thermometer.